Quantification of γ-nonalactone in botrytized and non-botrytized New Zealand and Australian wines

Abstract

To assess the effect of linoleic acid on the production of g-nonalactone in wine, fermentations with and without added linoleic acid were carried out in synthetic grape must (SGM) at 28 °C using commercial Saccharomyces cerevisiae EC1118. Prior toƴ-nonalactone quantitation in the finished wines and in a subset of six Australian and New Zealand commercial wines, several routes for the synthesis of a deuterated analogue ofƴ-nonalactone were attempted, before the deuterated d₆-analogue ofƴ-nonalactone from its non-deuterated analogue was produced successfully. Subsequently, attempts were made to utilise the d₆-ƴ-nonalactone analogue as an internal standard for the measurement of g-nonalactone using gas chromatography-mass spectrometry. However, the synthetic d₆-ƴ-nonalactone analogue proved to be an inappropriate internal standard for this purpose, due to back-exchange of deuterium atoms in wine. 2-Octanol was instead utilised as a surrogate internal standard for the measurement ofƴ-nonalactone.ƴ-Nonalactone was successfully identified (above the limit of detection, 4.12 g L^-1) in two commercial New Zealand botrytized wine samples, and one fermentation sample to which linoleic acid (132 mgL^-1) had been added. This suggests a possible link between the effect of Botrytis cinerea and/or linoleic acid, and increased levels ofƴ-nonalactone in wine. Further research is needed in this area to determine the mechanism ofƴ-nonalactone biosynthesis and to more accurately quantifyƴ-nonalactone in wine, using a more effective internal standard.